1. Field of the Invention
The present invention relates generally to electronic displays and in particular to LED control circuitry for back lighting LCD displays and the like.
2. Description of Related Art
Liquid crystal displays (LCD) are common type of electronic display. FIG. 1 shows a conventional LCD display which includes an LCD panel 20 which produces various pixels to define an image. A back light unit 24 operates to provide light to the LCD panel, with a light conductor plate 22 being disposed between the LCD panel and the back light unit 24. The back light unit 24 uses LEDs that provides improved power consumption, brightness and weight as compared to other back lighting devices such as cold cathode fluorescent lamps. In order to provide a color display, the LED backlighting unit may include a combination of red, green and blue (RGB) LEDs that are driven using what is termed the field sequential color (FSC) driving method. This method displays a color by relying upon the after image effect in human vision. As can be seen in the timing diagram of FIG. 2, one frame of image (or picture frame) divided into three sub-pictures (sub-frames). At the beginning of a typical picture frame, there is a Red sub-picture, followed by a Green sub-picture which is then followed by a Blue sub-picture. At the beginning of the Red sub-picture, the LCD panel 20 is refreshed and the Red LEDs in backlight unit 24 are driven. Thus, during the Red sub-picture, the Red components of the image is displayed. The same sequence is carried out during the subsequent Green and Blue sub-pictures. The separate color sub-pictures are not detected by the human eye, with the result being a full color image generally free of flicker.
Note that the LED backlight panel 24 of FIG. 1 is suited for relatively large LCD displays. For smaller displays, the backlighting LEDs are disposed on the edges of the LCD panel 20 so that the overall thickness of the display is substantially reduced. A light guide (not depicted) is than used diffused the light over the panel equally.
The circuitry for driving the LED backlight unit 24 using the FSC driving method is typically located in a circuit module separate from the unit itself. A typical circuit module may be in the form of an integrated circuit disposed in a integrated circuit package, with that package having a limited number of pins (electrical terminals) for interfacing with the LED unit 24 and other external circuit components.
There is a need for a circuit module for driving a LED backlight panel using the FSC driving method and other methods that requires only a limited number of pins but yet is capable of providing an optimized drive to the individual LEDs of the panel. As will become apparent to those skilled in the art after a reading of the following Detailed Description of the Invention together with the drawings, the present invention addresses these and other shortcomings of prior art LED driver circuits.